Shading of images using texture

Abstract

Colors are obtained and used to shade two-dimensional non-photo realistic images of three-dimensional models. The colors are stored as texels in texture maps. The texels are chosen to shade the images based on their orientation in a scene. The colors may be obtained once, in a pre-rendering process. The colors may then be selected in a run-time process.

1. A method of rendering a cartoon image based on a three-dimensional model organized as a plurality of polygons, each polygon defined by a set of vertices, the method comprising:
 providing a texture map having a plurality of texels, each texel having a color value that is determined using a set of virtual lighting parameters; 
 associating one or more threshold parameters with each texel in the texture map; 
 obtaining a texture coordinate for a vertex of a polygon based on a dot product of a surface normal to the vertex and a light vector between the vertex and a virtual light source, wherein obtaining a texture coordinate comprises interpolating values in texture space; 
 comparing the texture coordinate to a threshold parameter; 
 selecting one of the texels from the texture map based on comparison of the texture coordinate to the threshold parameter; and 
 rendering the cartoon image, wherein rendering comprises shading the polygon using the selected texel. 
 
     
     
       2. The method of  claim 1 , wherein an orientation of the image is established relative to the virtual light, source. 
     
     
       3. The method of  claim 1 , wherein one of the plurality of texels has a color value that represents an illuminated color for the image. 
     
     
       4. The method of  claim 3 , further comprising:
 processing the color value representing the illuminated color with a shadow factor to obtain a color value that represents a shadow color for the image. 
 
     
     
       5. The method of  claim 4 , further comprising storing the the color value that represents the shadow color as a texel in the texture map. 
     
     
       6. The method of  claim 1 , wherein determining is performed as a pre-rendering process and selecting is performed as a run-time process. 
     
     
       7. The method of  claim 1 , wherein the image comprises representations of a plurality of materials, each material having a texture map. 
     
     
       8. An article comprising a computer-readable medium that stores instructions for use in rendering a cartoon image based on a three-dimensional model organized as a plurality of polygons, each polygon defined by a set of vertices, the instructions for causing the computer to:
 provide a texture map having two or more texels, each texel having a color value that is determined using a set of virtual lighting parameters; 
 associate one or more threshold parameters with each texel in the texture map; 
 obtain a texture coordinate for a vertex of a polygon based on a dot product of a surface normal to the vertex and a light vector between the vertex and a virtual light source, wherein obtaining a texture coordinate comprises interpolating values in texture space; 
 compare the texture coordinate to a threshold parameter; 
 select one of the texels from the texture map based on comparison of the texture coordinate to the threshold parameter; and 
 render the cartoon image, wherein rendering the cartoon image comprises rendering the polygon using the selected texel. 
 
     
     
       9. The article of  claim 8 , wherein one of the plurality of texels has a color value that represents an illuminated color for the image. 
     
     
       10. The article of  claim 9 , further comprising instructions for causing the machine to:
 process the color value representing the illuminated color with a shadow factor to obtain a color value that represents a shadow color for the image. 
 
     
     
       11. The article of  claim 10 , further comprising instructions for causing the machine to store the color value that represents the shadow color as a texel in the texture map. 
     
     
       12. The article of  claim 8 , further comprising instructions for causing the machine to:
 determine color values for two or more texels for the texture map in a pre-rendering process; and 
 select one of the texels from the texture map in a run-time process. 
 
     
     
       13. The article of  claim 8 , wherein the image comprises representations of a plurality of materials, each material having a texture map. 
     
     
       14. An apparatus for use in rendering a cartoon image based on a three-dimensional model organized as a plurality of polygons, each polygon defined by a set of vertices, the apparatus comprising a memory which stores instructions and a processor that executes the instructions to:
 (i) provide a texture map having two or more texels, each texel having a color value that is determined using a set of virtual lighting parameters; 
 (ii) associate one or more threshold parameters with each texel in the texture map; 
 (iii) obtain a texture coordinate for a vertex of a polygon based on a dot product of a surface normal to the vertex and a light vector between the vertex and a virtual light source, wherein obtaining a texture coordinate comprises interpolating values in texture space; 
 (iv) compare the texture coordinate to a threshold parameter; 
 (v) select one of the texels from the texture map based on comparison of the texture coordinate to the threshold parameter; and 
 (vi) render the cartoon image, wherein rendering the cartoon image comprises rendering the polygon using the selected texel. 
 
     
     
       15. The apparatus of  claim 14 , wherein one of the plurality of texels has a color value that represents an illuminated color for the image. 
     
     
       16. The apparatus of  claim 14 , wherein the processor executes instructions to:
 process the color value representing the illuminated color with a shadow factor to obtain a color value that represents a shadow color for the image. 
 
     
     
       17. The apparatus of  claim 16 , wherein the processor executes instructions to store the color value that represents the shadow color as a texel in the texture map. 
     
     
       18. The apparatus of  claim 14 , wherein the processor executes instructions to:
 determine color values for two or more texels for the texture map in a pre-rendering process; and 
 select one of the texels from the texture map in a run-time process. 
 
     
     
       19. The apparatus of  claim 14 , wherein the image comprises representations of a plurality of materials, each material having a texture map. 
     
     
       20. The method of  claim 1 , further comprising:
 interpolating a hardedge between vertices of the polygon if the texture coordinate for the vertex of the polygon is different from a second texture coordinate for a second vertex of the polygon.